1. Field of the Invention
The present invention relates to a liquid discharge head for discharging a liquid and a method for manufacturing the same. Specifically, the present invention relates to an ink jet recording head, which is used for recording by discharging ink onto a recording medium, and a method for manufacturing the same.
2. Description of the Related Art
An ink jet recording head used in an ink jet recording system is an example of a liquid discharge head. An ink jet recording head generally has a passage, an energy generating element provided in the passage to generate the energy for discharging ink, and a fine ink discharge port (referred to as an “orifice”) for discharging ink onto some form of media, such as paper.
U.S. Pat. No. 4,657,631 discloses an example of a conventional method for manufacturing such an ink jet recording head. Specifically, it discloses forming a passage pattern using a photosensitive material on a substrate on which energy generating elements have already been formed, and then applying a coating resin layer as a passage forming member on the substrate so as to cover the pattern. Next, a discharge port is formed in the coating resin layer, and then the photosensitive material used for the pattern is removed. This method is capable of fine processing with a very high level of precision for forming the passage and the discharge port because it employs a photolithographic method used in semiconductor manufacturing.
A recently developing trend is for the ink jet recording heads to have a smaller orifice diameter in view of the need to discharge micro droplets. In this case, the following problems occur. The flow resistance of the ink in a micro discharge port and a discharge portion continuing therefrom is increased, adversely affecting the ink discharge. Also, there is an increase in the recovery (re-filling of ink) speed. In addition, when the viscosity of ink increases due to evaporation of the ink from the orifice in a standby mode, no discharge may occur at the initial stage of the discharge.
A known method for controlling the flow resistance and ink evaporation involves forming a so-called tapered discharge portion, the diameter of which decreases toward the orifice, as disclosed in U.S. Pat. No. 7,048,358.
It may be difficult, however, to desirably form such a tapered discharge portion, especially if its size is small enough to discharge micro droplets.
On the other hand, when the ink re-filling rate is increased, the time required for stabilizing a droplet meniscus on an orifice surface also tends to increase. In particular, this tendency becomes significant in a discharge portion for discharging large droplets. Therefore, a straight discharge portion in which the sectional area parallel to a substrate is the same as the orifice may be preferred according to the size of droplets.